In the environment of cleaning the surfaces of large structures such as fuel storage tanks, bridges, and other walled environments, it is known to use abrasive blasting systems for removal of dirty or contaminated surface finishes. It is also known to rig such blasting systems with flexible containment devices or portable rooms which isolate the area, and contain the dust and particulate material as it is being collected by vacuum systems. Generally such systems include a closed loop ventilation system whereby air is introduced to the containment area and withdrawn through at least one separator means for removal of abrasive and contaminated materials.
On-site abrasive cleaning processes produce large quantities of a portion of particulate materials, grit, and dust, a portion of which escapes into the atmosphere, collects on surrounding or adjacent surfaces, and is inhaled by workers. Such loss of containment is acceptable when non-hazardous materials are involved. However, where hazardous materials such as lead paint, asbestos, and the like are removed, the threat to the environment and the health of personnel is substantially greater.
The physical structure of prior systems conventionally is based on the vertical movement up and down the surface being cleaned one section at a time. Most are supported by cables, as in the staging type generally used for window cleaning; or, supported on scaffolding rigs which must be dismantled at least partially when moved from one section to another. With such riggings, any lateral (or horizontal relative to the work surface) movement of the structure is inhibited or eliminated.
Further problems related to prior art systems involve an inability to isolate a work area and enable the maintenance of a constant air pressure, and the maximum entrapment and evacuation of removed, frequently contaminated materials. In known systems the enclosure of the area is most often accomplished with sheet materials that are draped over the scaffolding and held in place with tie-downs and riggings much like those used with canopies and tents. Use of such loosely-formed enclosures prohibits the formation of a controlled air flow for ventilation or for entrapment of particulate material. Additionally, such enclosures are frequently subjected to high winds, which winds can become trapped and completely destroy the enclosure; often jeopardizing the safety and lives of operators. In known devices, when weather conditions change abruptly, it is virtually impossible to lower the enclosure rapidly and prevent damage and/or injury.
With regard to adequate containment of removed particulate materials, prior art devices utilizing suspension rigging or scaffolding have proven to be highly ineffective. While vacuum systems are employed, there remains a large amount of material which is not entrained in the vacuum and falls to the ground around the structure. This creates a necessity for secondary collection of residue, increasing the time and cost requirements for the operation. While such secondary collections previously were a problem only in increased time, there now exists a question of ground contamination from hazardous materials such as lead paint.
These same hazardous materials not only become ground contamination when they are improperly contained, but may also be found in blood samples taken periodically from operators.